PROJECT SUMMARY Innate lymphoid cells or ILCs are recently characterized constitutes of vertebrate immune system. They share a common lymphoid progenitor in bone marrow with T and B cells but lack antigen-specific receptors. ILCs localize in many tissues of both mice and humans but are enriched in barrier surfaces such as lung, gut and skin, where they directly respond to ?alarmin? cytokine signals released from inflamed or injured tissues. By producing an array of ?effecter? cytokines, ILCs initiate and amplify downstream immune reactions, thus are considered to be critical early protectors in host defense. Increasing evidence indicates that ILCs also play important roles in tissue remolding, metabolic homeostasis, inflammation and autoimmune disorders. My research vison is to understand the biological principles and molecular basis of ILC activation, migration, and their immunological functions. ILCs were generally believed to be tissue-resident cells and they don?t circulate even during infection. But this major concept of ILC has been completely changed by my recent discovery of a new ILC population, termed inflammatory or induced ILC2s, which migrate from the gut to the lung during helminth infection. Those findings establish a new paradigm of ILC biology: though ILCs, or ILC2s at a minimum, are largely tissue resident in the steady state, they become mobile during infection and contribute to distal immune protection. With this new paradigm, many fundamental questions on ILCs are to be answered. In the proposed five-year project, we aim to answer a few: 1) Do intestine-derived ILC2s modulate asthma? We hypothesize that repositioning of gut- derived iILC2s to the lung during parasitic infection dampens the allergic responses by conferring ?innate tolerance? to stronger asthmatic allergens. 2) Does microbiota modulate ILC2 activation and migration? We hypothesize that intestinal microbiota is essential for cytokine-induced ILC2 responses and commensal bacteria- derived metabolites provide a secondary signal that facilitates ILC2 activation and subsequent inter-organ trafficking. 3) Do existing drugs that target T cells have the capability to regulate the ILC function? We will perform a screening assay to identify such candidate drugs by using a gene reporter system that we have generated. Successful completion of the proposed studies will lead to a fundamental understanding of molecular mechanisms that underlie ILC2 activation, ILC2 migration, ILC2 repositioning-mediated protection against allergic asthma, and microbiota-ILC2 interaction. The knowledge to be gained will contribute to the development of novel therapeutic approaches for asthma and other inflammatory and infectious diseases. The existing drug screening will enhance the reconsideration of drug usage in clinic. Multi-disciplinary approaches will be employed including high-parameter flow cytometry, single-cell(sc) RNA-Seq, scATAC-Seq, multiplex 3D tissue imaging and genetic mouse models. This is a research complex of immune cell biology, molecular biology, system immunology and host-pathogen interaction. Columbia University Medical Center provides enormous research resources and great opportunities for collaborations that will make it possible.